The present invention is directed to systems and devices related to the design and formation of surgical implants such as surgical linking devices. More particularly the present invention provides a system and devices for forming or shaping a surgical implant to conform to two or more selected attachment points (including surface anatomy) in a six degree of freedom method for attachment.
Fixation systems for aligning, adjusting and or fixing, either partially or rigidly, portions of a patient's bony anatomy in a desired spatial relationship relative to each other are frequently used in orthopedic surgery. For example, in spinal surgery for repair or positional adjustment of the vertebrae, it is often necessary that multiple vertebrae are surgically manipulated. As spinal surgery often requires the instrumentation of more bony elements than other areas of orthopedic surgery, the linkage devices can be extremely challenging to design and implant. Treatment for conditions such as scoliosis, spinal injury, disk problems and the like often make use of spinal rod fixation systems for positioning the vertebrae and supporting the spinal motion segments.
A spinal rod needs to be oriented in six degrees of freedom to compensate for the anatomical structure of the particular patient's spine and the particular attachment points or methods for attaching the rods to the vertebrae. In addition, the physiological problem being treated as well as physician's preferences will determine the exact configuration necessary. Accordingly, the size, length and particular bends of each spinal rod depends on the size, number and position of each vertebra to be constrained, their spatial relationship as well as the fixating means, such as pedicle screws, used to hold the rods attached to each vertebra. The relationship of the vertebrae will be different for each patient and the positioning of the patient at the point of installation of the rods. During surgery, the orientation of the spine and vertebrae can be very different than the corresponding position of a patient's upright posture. Rods are bent in one or more anatomic planes measured by distance from each bend, angle of the bend and rotation in relationship to other bend points in order to fit into two or more vertebral anchors.
The bending of a spinal rod can be accomplished by a number of methods. The oldest and most widely used method for bending rods manually during surgery is a three-point bender called a French Bender in which a bending pliers type device is manually operated to place one or more bends in a rod. The French Bender requires both hands to operate and provides leverage based on the length of the handle. While the device can make it relatively easy to bend a spinal rod, the determination of the location, angle and rotation of bends using such a device is often arbitrary. Problems can thus occur from bending a device and then rebending to fix mistakes which impose metal fatigue or stress risers into a rod thus increasing the risk of a mechanical failure. Increased time in the operating room (OR) to achieve optimum bending of the rod can increase the chance of morbidity.
Spinal rods are usually formed of stainless steel, titanium or other similarly hard metal, and as such are difficult to bend without some sort of leverage-based bender. In addition, since several spatial relationships have to be maintained in using a French Bender, the process can take an extremely long time and its use requires a great degree of physician skill to accomplish an accurate final product. Even still it is difficult to achieve a well-shaped rod using the French Bender. Accordingly, various ways have been attempted to overcome the limitations of the current technology.
A number of manual benders are described in the art. In U.S. Pat. No. 5,113,685 issued May 19, 1992 to Asher et al, there is described an apparatus for use in bending rods and plates to the spinal column comprising an elongated bar with a variety of bending angles for bending more angles than the French Bender. However, this device is hard to use and provides no means for determining the six degrees of spatial relationship that each bend must make. In US patent application 2006/0150699 published Jul. 13, 2006 to Garner, et al, there is an instrument and method for bending rod using a lever pliers type device having bearing surfaces. In addition, the angle of bend can be determined by use of a gauge that indicates angle bend by degree of grip movement. While this device may be easier to use, it does not aid in determination of the other degrees of freedom either in calculating them or in making the final bends.
An automatic method designed for pre-surgical formation of spinal rods is disclosed in US patent application 2005/0262911 published Dec. 1, 2005 to Dankowicz, et al. An automatic series of shaping steps is “imposed” on a rod from an input mechanism for producing the desired multi-dimensional bent shape. One problem with this device is that it relies on a pre-surgical determination of the points at which bends occur to determine the final shape of the rod. While it is possible to anticipate where the anchors might ideally end up and occasionally be correct, surgical implantation of attachment points is as much art as science so a preformed rod may not be accurately produced when compared to the anchor means as they are actually installed in the spine. This can lead to a highly problematic circumstance in which the surgical site has been opened and the surgeon has a rod that does not fit the attachment points. Further disadvantages are that the device is large and that some surgeons still would prefer a manual means of producing a rod during surgery because of the ability to make minute adjustments based on feedback during surgery.
Effort has been directed to computer-aided design or shaping of spinal rods, but these efforts have been largely unsuccessful due to the lack of bending devices as well as a lack of understanding of all the issues involved in bending surgical devices. For example, an article entitled “A pilot study on computer-assisted optimal contouring of orthopedic fixation devices,” Computer Aided Surgery, 1999; 4 (6):305-13, indicated that overcoming these problems would be difficult if not impossible.
Image guided surgical systems, for example, devices produced by BrainLAB, as well as three dimensional digitizers are already in the art and some are already FDA approved for use during surgery. These devices are fairly commonly used by some physicians in the operating environment. By moving the digitizer through space or inputting a particular point in space, a map can be produced of spatial relationships. In U.S. Pat. No. 6,400,131, issued on Dec. 31, 2002 to Leitner et al., there is described a contour mapping system applicable as a spine analyzer and probe. The device is disclosed as being used to determine the curvature of the spine while standing and contour mapping of the spine in the intact (non-surgical) patient.
Accordingly, a means for designing and forming a surgical linking device, especially for linking bony parts of the body, for use in a surgical orthopedic procedure such as the attachment of a spinal rod, that is accurate, quick and takes the various input characteristics into account for the specific implanted device as actually needed would be of great value during an orthopedic implant surgery such as spinal surgery.